Question

java.lang.Object
  └java.lang.StringBuilder

所有已实现的接口：

Serializable, Appendable, CharSequence

---

public final class StringBuilder

extends Object

implements Serializable, CharSequence

一个可变的字符序列。此类提供一个与 StringBuffer 兼容的 API，但不保证同步。该类被设计用作 StringBuffer 的一个简易替换，用在字符串缓冲区被单个线程使用的时候（这种情况很普遍）。如果可能，建议优先采用该类，因为在大多数实现中，它比 StringBuffer 要快。

在 StringBuilder 上的主要操作是 append 和 insert 方法，可重载这些方法，以接受任意类型的数据。每个方法都能有效地将给定的数据转换成字符串，然后将该字符串的字符追加或插入到字符串生成器中。 append 方法始终将这些字符添加到生成器的末端；而 insert 方法则在指定的点添加字符。

例如，如果 z 引用一个当前内容为“ start ”的字符串生成器对象，则该方法调用 z.append("le") 将使字符串生成器包含“ startle ”，而 z.insert(4, "le") 将更改字符串生成器，使之包含“ starlet ”。

通常，如果 sb 引用 StringBuilder 的实例，则 sb.append(x) 和 sb.insert(sb.length(),x) 具有相同的效果。 每个字符串生成器都有一定的容量。只要字符串生成器所包含的字符序列的长度没有超出此容量，就无需分配新的内部缓冲区。如果内部缓冲区溢出，则此容量自动增大。

将 StringBuilder 的实例用于多个线程是不安全的。如果需要这样的同步，则建议使用 StringBuffer 。

 

从以下版本开始：

1.5

另请参见：

StringBuffer , String , 序列化表格

---

 

构造方法摘要
StringBuilder() 构造一个其中不带字符的字符串生成器，初始容量为 16 个字符。
StringBuilder(CharSequenceseq) 构造一个字符串生成器，包含与指定的 CharSequence 相同的字符。
StringBuilder(intcapacity) 构造一个其中不带字符的字符串生成器，初始容量由 capacity 参数指定。
StringBuilder(Stringstr) 构造一个字符串生成器，并初始化为指定的字符串内容。

方法摘要
StringBuilder	append(booleanb) Appends the string representation of the boolean argument to the sequence.
StringBuilder	append(charc) Appends the string representation of the char argument to this sequence.
StringBuilder	append(char[]str) Appends the string representation of the char array argument to this sequence.
StringBuilder	append(char[]str, intoffset, intlen) Appends the string representation of a subarray of the char array argument to this sequence.
StringBuilder	append(CharSequences) 向此 Appendable 追加指定的字符序列。
StringBuilder	append(CharSequences, intstart, intend) Appends a subsequence of the specified CharSequence to this sequence.
StringBuilder	append(doubled) Appends the string representation of the double argument to this sequence.
StringBuilder	append(floatf) Appends the string representation of the float argument to this sequence.
StringBuilder	append(inti) Appends the string representation of the int argument to this sequence.
StringBuilder	append(longlng) Appends the string representation of the long argument to this sequence.
StringBuilder	append(Objectobj) Appends the string representation of the Object argument.
StringBuilder	append(Stringstr) Appends the specified string to this character sequence.
StringBuilder	append(StringBuffersb) 将指定的 StringBuffer 追加到此序列。
StringBuilder	appendCodePoint(intcodePoint) Appends the string representation of the codePoint argument to this sequence.
int	capacity() Returns the current capacity.
char	charAt(intindex) Returns the char value in this sequence at the specified index.
int	codePointAt(intindex) Returns the character (Unicode code point) at the specified index.
int	codePointBefore(intindex) Returns the character (Unicode code point) before the specified index.
int	codePointCount(intbeginIndex, intendIndex) Returns the number of Unicode code points in the specified text range of this sequence.
StringBuilder	delete(intstart, intend) Removes the characters in a substring of this sequence.
StringBuilder	deleteCharAt(intindex) Removes the char at the specified position in this sequence.
void	ensureCapacity(intminimumCapacity) Ensures that the capacity is at least equal to the specified minimum.
void	getChars(intsrcBegin, intsrcEnd, char[]dst, intdstBegin) Characters are copied from this sequence into the destination character array dst .
int	indexOf(Stringstr) Returns the index within this string of the first occurrence of the specified substring.
int	indexOf(Stringstr, intfromIndex) Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.
StringBuilder	insert(intoffset, booleanb) Inserts the string representation of the boolean argument into this sequence.
StringBuilder	insert(intoffset, charc) Inserts the string representation of the char argument into this sequence.
StringBuilder	insert(intoffset, char[]str) Inserts the string representation of the char array argument into this sequence.
StringBuilder	insert(intindex, char[]str, intoffset, intlen) Inserts the string representation of a subarray of the str array argument into this sequence.
StringBuilder	insert(intdstOffset, CharSequences) Inserts the specified CharSequence into this sequence.
StringBuilder	insert(intdstOffset, CharSequences, intstart, intend) Inserts a subsequence of the specified CharSequence into this sequence.
StringBuilder	insert(intoffset, doubled) Inserts the string representation of the double argument into this sequence.
StringBuilder	insert(intoffset, floatf) Inserts the string representation of the float argument into this sequence.
StringBuilder	insert(intoffset, inti) Inserts the string representation of the second int argument into this sequence.
StringBuilder	insert(intoffset, longl) Inserts the string representation of the long argument into this sequence.
StringBuilder	insert(intoffset, Objectobj) Inserts the string representation of the Object argument into this character sequence.
StringBuilder	insert(intoffset, Stringstr) Inserts the string into this character sequence.
int	lastIndexOf(Stringstr) Returns the index within this string of the rightmost occurrence of the specified substring.
int	lastIndexOf(Stringstr, intfromIndex) Returns the index within this string of the last occurrence of the specified substring.
int	length() Returns the length (character count).
int	offsetByCodePoints(intindex, intcodePointOffset) Returns the index within this sequence that is offset from the given index by codePointOffset code points.
StringBuilder	replace(intstart, intend, Stringstr) Replaces the characters in a substring of this sequence with characters in the specified String .
StringBuilder	reverse() Causes this character sequence to be replaced by the reverse of the sequence.
void	setCharAt(intindex, charch) The character at the specified index is set to ch .
void	setLength(intnewLength) Sets the length of the character sequence.
CharSequence	subSequence(intstart, intend) Returns a new character sequence that is a subsequence of this sequence.
String	substring(intstart) Returns a new String that contains a subsequence of characters currently contained in this character sequence.
String	substring(intstart, intend) Returns a new String that contains a subsequence of characters currently contained in this sequence.
String	toString() Returns a string representing the data in this sequence.
void	trimToSize() Attempts to reduce storage used for the character sequence.

从类 java.lang.Object 继承的方法
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

从接口 java.lang.CharSequence 继承的方法
charAt, length, subSequence

 

构造方法详细信息

StringBuilder

public StringBuilder()

构造一个其中不带字符的字符串生成器，初始容量为 16 个字符。

---

StringBuilder

public StringBuilder(intcapacity)

构造一个其中不带字符的字符串生成器，初始容量由 capacity 参数指定。

参数：

capacity - 初始容量。

抛出：

NegativeArraySizeException - 如果 capacity 参数小于 0 。

---

StringBuilder

public StringBuilder(Stringstr)

构造一个字符串生成器，并初始化为指定的字符串内容。该字符串生成器的初始容量为 16 加上字符串参数的长度。

参数：

str - 缓冲区的初始内容。

抛出：

NullPointerException - 如果 str 为 null

---

StringBuilder

public StringBuilder(CharSequenceseq)

构造一个字符串生成器，包含与指定的 CharSequence 相同的字符。该字符串生成器的初始容量为 16 加上 CharSequence 参数的长度。

参数：

seq - 要复制的序列。

抛出：

NullPointerException - 如果 seq 为 null

方法详细信息

append

public StringBuilder append(Objectobj)

Appends the string representation of the Object argument.

The argument is converted to a string as if by the method String.valueOf , and the characters of that string are then appended to this sequence.

参数：

obj - an Object .

返回：

a reference to this object.

另请参见：

String.valueOf(java.lang.Object) , append(java.lang.String)

---

append

public StringBuilder append(Stringstr)

Appends the specified string to this character sequence.

The characters of the String argument are appended, in order, increasing the length of this sequence by the length of the argument. If str is null , then the four characters "null" are appended.

Let n be the length of this character sequence just prior to execution of the append method. Then the character at index k in the new character sequence is equal to the character at index k in the old character sequence, if k is less than n; otherwise, it is equal to the character at index k-n in the argument str .

参数：

str - a string.

返回：

a reference to this object.

---

append

public StringBuilder append(StringBuffersb)

将指定的 StringBuffer 追加到此序列。

按顺序将 StringBuffer 参数中的字符追加到该序列中，使该序列在长度上增加该参数的长度。如果 sb 为 null ，则向该序列中追加 4 个 "null" 字符。

在执行 append 方法前，让此字符序列的长度为 n。如果 k 小于 n，则新字符序列中索引 k 处的字符等于原有序列中索引 k 处的字符；否则它等于参数 sb 中索引 k-n 处的字符。

参数：

sb - 要追加的 StringBuffer 。

返回：

此对象的一个引用。

---

append

public StringBuilder append(CharSequences)

从接口 Appendable 复制的描述

向此 Appendable 追加指定的字符序列。

有时可能没有追加整个序列，这取决于使用哪个类来实现字符序列 csq 。例如，如果 csq 是 CharBuffer 的一个实例，则通过缓冲区的位置和限制来定义要追加的子序列。

指定者：

接口 Appendable 中的 append

参数：

s - 要追加的字符串序列。如果 csq 为 null ，则向该 Appendable 追加四个字符 "null" 。

返回：

此 Appendable 的引用

抛出：

IndexOutOfBoundsException

---

append

public StringBuilder append(CharSequences,
                            intstart,
                            intend)

Appends a subsequence of the specified CharSequence to this sequence.

Characters of the argument s , starting at index start , are appended, in order, to the contents of this sequence up to the (exclusive) index end . The length of this sequence is increased by the value of end - start .

Let n be the length of this character sequence just prior to execution of the append method. Then the character at index k in this character sequence becomes equal to the character at index k in this sequence, if k is less than n; otherwise, it is equal to the character at index k+start-n in the argument s .

If s is null , then this method appends characters as if the s parameter was a sequence containing the four characters "null" .

指定者：

接口 Appendable 中的 append

参数：

s - the sequence to append.

start - the starting index of the subsequence to be appended.

end - the end index of the subsequence to be appended.

返回：

a reference to this object.

抛出：

IndexOutOfBoundsException - if start or end are negative, or start is greater than end or end is greater than s.length()

---

append

public StringBuilder append(char[]str)

Appends the string representation of the char array argument to this sequence.

The characters of the array argument are appended, in order, to the contents of this sequence. The length of this sequence increases by the length of the argument.

The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(char[]) and the characters of that string were then appended to this character sequence.

参数：

str - the characters to be appended.

返回：

a reference to this object.

---

append

public StringBuilder append(char[]str,
                            intoffset,
                            intlen)

Appends the string representation of a subarray of the char array argument to this sequence.

Characters of the char array str , starting at index offset , are appended, in order, to the contents of this sequence. The length of this sequence increases by the value of len .

The overall effect is exactly as if the arguments were converted to a string by the method String.valueOf(char[],int,int) and the characters of that string were then appended to this character sequence.

参数：

str - the characters to be appended.

offset - the index of the first char to append.

len - the number of char s to append.

返回：

a reference to this object.

---

append

public StringBuilder append(booleanb)

Appends the string representation of the boolean argument to the sequence.

The argument is converted to a string as if by the method String.valueOf , and the characters of that string are then appended to this sequence.

参数：

b - a boolean .

返回：

a reference to this object.

另请参见：

String.valueOf(boolean) , append(java.lang.String)

---

append

public StringBuilder append(charc)

Appends the string representation of the char argument to this sequence.

The argument is appended to the contents of this sequence. The length of this sequence increases by 1 .

The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(char) and the character in that string were then appended to this character sequence.

指定者：

接口 Appendable 中的 append

参数：

c - a char .

返回：

a reference to this object.

---

append

public StringBuilder append(inti)

Appends the string representation of the int argument to this sequence.

The argument is converted to a string as if by the method String.valueOf , and the characters of that string are then appended to this sequence.

参数：

i - an int .

返回：

a reference to this object.

另请参见：

String.valueOf(int) , append(java.lang.String)

---

append

public StringBuilder append(longlng)

Appends the string representation of the long argument to this sequence.

The argument is converted to a string as if by the method String.valueOf , and the characters of that string are then appended to this sequence.

参数：

lng - a long .

返回：

a reference to this object.

另请参见：

String.valueOf(long) , append(java.lang.String)

---

append

public StringBuilder append(floatf)

Appends the string representation of the float argument to this sequence.

The argument is converted to a string as if by the method String.valueOf , and the characters of that string are then appended to this string sequence.

参数：

f - a float .

返回：

a reference to this object.

另请参见：

String.valueOf(float) , append(java.lang.String)

---

append

public StringBuilder append(doubled)

Appends the string representation of the double argument to this sequence.

The argument is converted to a string as if by the method String.valueOf , and the characters of that string are then appended to this sequence.

参数：

d - a double .

返回：

a reference to this object.

另请参见：

String.valueOf(double) , append(java.lang.String)

---

appendCodePoint

public StringBuilder appendCodePoint(intcodePoint)

Appends the string representation of the codePoint argument to this sequence.

The argument is appended to the contents of this sequence. The length of this sequence increases by Character.charCount(codePoint) .

The overall effect is exactly as if the argument were converted to a char array by the method Character.toChars(int) and the character in that array were then appended to this character sequence.

参数：

codePoint - a Unicode code point

返回：

a reference to this object.

从以下版本开始：

1.5

---

delete

public StringBuilder delete(intstart,
                            intend)

Removes the characters in a substring of this sequence. The substring begins at the specified start and extends to the character at index end - 1 or to the end of the sequence if no such character exists. If start is equal to end , no changes are made.

参数：

start - The beginning index, inclusive.

end - The ending index, exclusive.

返回：

This object.

抛出：

StringIndexOutOfBoundsException - if start is negative, greater than length() , or greater than end .

---

deleteCharAt

public StringBuilder deleteCharAt(intindex)

Removes the char at the specified position in this sequence. This sequence is shortened by one char .

Note: If the character at the given index is a supplementary character, this method does not remove the entire character. If correct handling of supplementary characters is required, determine the number of char s to remove by calling Character.charCount(thisSequence.codePointAt(index)) , where thisSequence is this sequence.

参数：

index - Index of char to remove

返回：

This object.

抛出：

StringIndexOutOfBoundsException - if the index is negative or greater than or equal to length() .

---

replace

public StringBuilder replace(intstart,
                             intend,
                             Stringstr)

Replaces the characters in a substring of this sequence with characters in the specified String . The substring begins at the specified start and extends to the character at index end - 1 or to the end of the sequence if no such character exists. First the characters in the substring are removed and then the specified String is inserted at start . (This sequence will be lengthened to accommodate the specified String if necessary.)

参数：

start - The beginning index, inclusive.

end - The ending index, exclusive.

str - String that will replace previous contents.

返回：

This object.

抛出：

StringIndexOutOfBoundsException - if start is negative, greater than length() , or greater than end .

---

insert

public StringBuilder insert(intindex,
                            char[]str,
                            intoffset,
                            intlen)

Inserts the string representation of a subarray of the str array argument into this sequence. The subarray begins at the specified offset and extends len char s. The characters of the subarray are inserted into this sequence at the position indicated by index . The length of this sequence increases by len char s.

参数：

index - position at which to insert subarray.

str - A char array.

offset - the index of the first char in subarray to be inserted.

len - the number of char s in the subarray to be inserted.

返回：

This object

抛出：

StringIndexOutOfBoundsException - if index is negative or greater than length() , or offset or len are negative, or (offset+len) is greater than str.length .

---

insert

public StringBuilder insert(intoffset,
                            Objectobj)

Inserts the string representation of the Object argument into this character sequence.

The second argument is converted to a string as if by the method String.valueOf , and the characters of that string are then inserted into this sequence at the indicated offset.

The offset argument must be greater than or equal to 0 , and less than or equal to the length of this sequence.

参数：

offset - the offset.

obj - an Object .

返回：

a reference to this object.

抛出：

StringIndexOutOfBoundsException - if the offset is invalid.

另请参见：

String.valueOf(java.lang.Object) , insert(int, java.lang.String) , length()

---

insert

public StringBuilder insert(intoffset,
                            Stringstr)

Inserts the string into this character sequence.

The characters of the String argument are inserted, in order, into this sequence at the indicated offset, moving up any characters originally above that position and increasing the length of this sequence by the length of the argument. If str is null , then the four characters "null" are inserted into this sequence.

The character at index k in the new character sequence is equal to:

• the character at index k in the old character sequence, if k is less than offset
• the character at index k-offset in the argument str , if k is not less than offset but is less than offset+str.length()
• the character at index k-str.length() in the old character sequence, if k is not less than offset+str.length()

The offset argument must be greater than or equal to 0 , and less than or equal to the length of this sequence.

参数：

offset - the offset.

str - a string.

返回：

a reference to this object.

抛出：

StringIndexOutOfBoundsException - if the offset is invalid.

另请参见：

length()

---

insert

public StringBuilder insert(intoffset,
                            char[]str)

Inserts the string representation of the char array argument into this sequence.

The characters of the array argument are inserted into the contents of this sequence at the position indicated by offset . The length of this sequence increases by the length of the argument.

The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(char[]) and the characters of that string were then inserted into this character sequence at the position indicated by offset .

参数：

offset - the offset.

str - a character array.

返回：

a reference to this object.

抛出：

StringIndexOutOfBoundsException - if the offset is invalid.

---

insert

public StringBuilder insert(intdstOffset,
                            CharSequences)

Inserts the specified CharSequence into this sequence.

The characters of the CharSequence argument are inserted, in order, into this sequence at the indicated offset, moving up any characters originally above that position and increasing the length of this sequence by the length of the argument s.

The result of this method is exactly the same as if it were an invocation of this object's insert(dstOffset, s, 0, s.length()) method.

If s is null , then the four characters "null" are inserted into this sequence.

参数：

dstOffset - the offset.

s - the sequence to be inserted

返回：

a reference to this object.

抛出：

IndexOutOfBoundsException - if the offset is invalid.

---

insert

public StringBuilder insert(intdstOffset,
                            CharSequences,
                            intstart,
                            intend)

Inserts a subsequence of the specified CharSequence into this sequence.

The subsequence of the argument s specified by start and end are inserted, in order, into this sequence at the specified destination offset, moving up any characters originally above that position. The length of this sequence is increased by end - start .

The character at index k in this sequence becomes equal to:

• the character at index k in this sequence, if k is less than dstOffset
• the character at index k+start-dstOffset in the argument s , if k is greater than or equal to dstOffset but is less than dstOffset+end-start
• the character at index k-(end-start) in this sequence, if k is greater than or equal to dstOffset+end-start

The dstOffset argument must be greater than or equal to 0 , and less than or equal to the length of this sequence.

The start argument must be nonnegative, and not greater than end .

The end argument must be greater than or equal to start , and less than or equal to the length of s.

If s is null , then this method inserts characters as if the s parameter was a sequence containing the four characters "null" .

参数：

dstOffset - the offset in this sequence.

s - the sequence to be inserted.

start - the starting index of the subsequence to be inserted.

end - the end index of the subsequence to be inserted.

返回：

a reference to this object.

抛出：

IndexOutOfBoundsException - if dstOffset is negative or greater than this.length() , or start or end are negative, or start is greater than end or end is greater than s.length()

---

insert

public StringBuilder insert(intoffset,
                            booleanb)

Inserts the string representation of the boolean argument into this sequence.

The second argument is converted to a string as if by the method String.valueOf , and the characters of that string are then inserted into this sequence at the indicated offset.

The offset argument must be greater than or equal to 0 , and less than or equal to the length of this sequence.

参数：

offset - the offset.

b - a boolean .

返回：

a reference to this object.

抛出：

StringIndexOutOfBoundsException - if the offset is invalid.

另请参见：

String.valueOf(boolean) , insert(int, java.lang.String) , length()

---

insert

public StringBuilder insert(intoffset,
                            charc)

Inserts the string representation of the char argument into this sequence.

The second argument is inserted into the contents of this sequence at the position indicated by offset . The length of this sequence increases by one.

The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(char) and the character in that string were then inserted into this character sequence at the position indicated by offset .

The offset argument must be greater than or equal to 0 , and less than or equal to the length of this sequence.

参数：

offset - the offset.

c - a char .

返回：

a reference to this object.

抛出：

IndexOutOfBoundsException - if the offset is invalid.

另请参见：

length()

---

insert

public StringBuilder insert(intoffset,
                            inti)

Inserts the string representation of the second int argument into this sequence.

The second argument is converted to a string as if by the method String.valueOf , and the characters of that string are then inserted into this sequence at the indicated offset.

The offset argument must be greater than or equal to 0 , and less than or equal to the length of this sequence.

参数：

offset - the offset.

i - an int .

返回：

a reference to this object.

抛出：

StringIndexOutOfBoundsException - if the offset is invalid.

另请参见：

String.valueOf(int) , insert(int, java.lang.String) , length()

---

insert

public StringBuilder insert(intoffset,
                            longl)

Inserts the string representation of the long argument into this sequence.

The second argument is converted to a string as if by the method String.valueOf , and the characters of that string are then inserted into this sequence at the position indicated by offset .

The offset argument must be greater than or equal to 0 , and less than or equal to the length of this sequence.

参数：

offset - the offset.

l - a long .

返回：

a reference to this object.

抛出：

StringIndexOutOfBoundsException - if the offset is invalid.

另请参见：

String.valueOf(long) , insert(int, java.lang.String) , length()

---

insert

public StringBuilder insert(intoffset,
                            floatf)

Inserts the string representation of the float argument into this sequence.

The second argument is converted to a string as if by the method String.valueOf , and the characters of that string are then inserted into this sequence at the indicated offset.

The offset argument must be greater than or equal to 0 , and less than or equal to the length of this sequence.

参数：

offset - the offset.

f - a float .

返回：

a reference to this object.

抛出：

StringIndexOutOfBoundsException - if the offset is invalid.

另请参见：

String.valueOf(float) , insert(int, java.lang.String) , length()

---

insert

public StringBuilder insert(intoffset,
                            doubled)

Inserts the string representation of the double argument into this sequence.

The second argument is converted to a string as if by the method String.valueOf , and the characters of that string are then inserted into this sequence at the indicated offset.

The offset argument must be greater than or equal to 0 , and less than or equal to the length of this sequence.

参数：

offset - the offset.

d - a double .

返回：

a reference to this object.

抛出：

StringIndexOutOfBoundsException - if the offset is invalid.

另请参见：

String.valueOf(double) , insert(int, java.lang.String) , length()

---

indexOf

public int indexOf(Stringstr)

Returns the index within this string of the first occurrence of the specified substring. The integer returned is the smallest value k such that:

 this.toString().startsWith(str, k)

is true .

参数：

str - any string.

返回：

if the string argument occurs as a substring within this object, then the index of the first character of the first such substring is returned; if it does not occur as a substring, -1 is returned.

抛出：

NullPointerException - if str is null .

---

indexOf

public int indexOf(Stringstr,
                   intfromIndex)

Returns the index within this string of the first occurrence of the specified substring, starting at the specified index. The integer returned is the smallest value k for which:

     k >= Math.min(fromIndex, str.length()) &&
                   this.toString().startsWith(str, k)

If no such value of k exists, then -1 is returned.

参数：

str - the substring for which to search.

fromIndex - the index from which to start the search.

返回：

the index within this string of the first occurrence of the specified substring, starting at the specified index.

抛出：

NullPointerException - if str is null .

---

lastIndexOf

public int lastIndexOf(Stringstr)

Returns the index within this string of the rightmost occurrence of the specified substring. The rightmost empty string "" is considered to occur at the index value this.length() . The returned index is the largest value k such that

 this.toString().startsWith(str, k)

is true.

参数：

str - the substring to search for.

返回：

if the string argument occurs one or more times as a substring within this object, then the index of the first character of the last such substring is returned. If it does not occur as a substring, -1 is returned.

抛出：

NullPointerException - if str is null .

---

lastIndexOf

public int lastIndexOf(Stringstr,
                       intfromIndex)

Returns the index within this string of the last occurrence of the specified substring. The integer returned is the largest value k such that:

     k <= Math.min(fromIndex, str.length()) &&
                   this.toString().startsWith(str, k)

If no such value of k exists, then -1 is returned.

参数：

str - the substring to search for.

fromIndex - the index to start the search from.

返回：

the index within this sequence of the last occurrence of the specified substring.

抛出：

NullPointerException - if str is null .

---

reverse

public StringBuilder reverse()

Causes this character sequence to be replaced by the reverse of the sequence. If there are any surrogate pairs included in the sequence, these are treated as single characters for the reverse operation. Thus, the order of the high-low surrogates is never reversed. Let n be the character length of this character sequence (not the length in char values) just prior to execution of the reverse method. Then the character at index k in the new character sequence is equal to the character at index n-k-1 in the old character sequence.

Note that the reverse operation may result in producing surrogate pairs that were unpaired low-surrogates and high-surrogates before the operation. For example, reversing "\uDC00\uD800" produces "\uD800\uDC00" which is a valid surrogate pair.

返回：

a reference to this object.

---

toString

public String toString()

Returns a string representing the data in this sequence. A new String object is allocated and initialized to contain the character sequence currently represented by this object. This String is then returned. Subsequent changes to this sequence do not affect the contents of the String .

指定者：

接口 CharSequence 中的 toString

返回：

a string representation of this sequence of characters.

---

length

public int length()

Returns the length (character count).

指定者：

接口 CharSequence 中的 length

返回：

the length of the sequence of characters currently represented by this object

---

capacity

public int capacity()

Returns the current capacity. The capacity is the amount of storage available for newly inserted characters, beyond which an allocation will occur.

返回：

the current capacity

---

ensureCapacity

public void ensureCapacity(intminimumCapacity)

Ensures that the capacity is at least equal to the specified minimum. If the current capacity is less than the argument, then a new internal array is allocated with greater capacity. The new capacity is the larger of:

• The minimumCapacity argument.
• Twice the old capacity, plus 2 .

If the minimumCapacity argument is nonpositive, this method takes no action and simply returns.

参数：

minimumCapacity - the minimum desired capacity.

---

trimToSize

public void trimToSize()

Attempts to reduce storage used for the character sequence. If the buffer is larger than necessary to hold its current sequence of characters, then it may be resized to become more space efficient. Calling this method may, but is not required to, affect the value returned by a subsequent call to the capacity() method.

---

setLength

public void setLength(intnewLength)

Sets the length of the character sequence. The sequence is changed to a new character sequence whose length is specified by the argument. For every nonnegative index k less than newLength , the character at index k in the new character sequence is the same as the character at index k in the old sequence if k is less than the length of the old character sequence; otherwise, it is the null character '\u0000' . In other words, if the newLength argument is less than the current length, the length is changed to the specified length.

If the newLength argument is greater than or equal to the current length, sufficient null characters ( '\u0000' ) are appended so that length becomes the newLength argument.

The newLength argument must be greater than or equal to 0 .

参数：

newLength - the new length

抛出：

IndexOutOfBoundsException - if the newLength argument is negative.

---

charAt

public char charAt(intindex)

Returns the char value in this sequence at the specified index. The first char value is at index 0 , the next at index 1 , and so on, as in array indexing.

The index argument must be greater than or equal to 0 , and less than the length of this sequence.

If the char value specified by the index is a surrogate, the surrogate value is returned.

指定者：

接口 CharSequence 中的 charAt

参数：

index - the index of the desired char value.

返回：

the char value at the specified index.

抛出：

IndexOutOfBoundsException - if index is negative or greater than or equal to length() .

---

codePointAt

public int codePointAt(intindex)

Returns the character (Unicode code point) at the specified index. The index refers to char values (Unicode code units) and ranges from 0 to length()- 1 .

If the char value specified at the given index is in the high-surrogate range, the following index is less than the length of this sequence, and the char value at the following index is in the low-surrogate range, then the supplementary code point corresponding to this surrogate pair is returned. Otherwise, the char value at the given index is returned.

参数：

index - the index to the char values

返回：

the code point value of the character at the index

抛出：

IndexOutOfBoundsException - if the index argument is negative or not less than the length of this sequence.

---

codePointBefore

public int codePointBefore(intindex)

Returns the character (Unicode code point) before the specified index. The index refers to char values (Unicode code units) and ranges from 1 to length() .

If the char value at (index - 1) is in the low-surrogate range, (index - 2) is not negative, and the char value at (index - 2) is in the high-surrogate range, then the supplementary code point value of the surrogate pair is returned. If the char value at index - 1 is an unpaired low-surrogate or a high-surrogate, the surrogate value is returned.

参数：

index - the index following the code point that should be returned

返回：

the Unicode code point value before the given index.

抛出：

IndexOutOfBoundsException - if the index argument is less than 1 or greater than the length of this sequence.

---

codePointCount

public int codePointCount(intbeginIndex,
                          intendIndex)

Returns the number of Unicode code points in the specified text range of this sequence. The text range begins at the specified beginIndex and extends to the char at index endIndex - 1 . Thus the length (in char s) of the text range is endIndex-beginIndex . Unpaired surrogates within this sequence count as one code point each.

参数：

beginIndex - the index to the first char of the text range.

endIndex - the index after the last char of the text range.

返回：

the number of Unicode code points in the specified text range

抛出：

IndexOutOfBoundsException - if the beginIndex is negative, or endIndex is larger than the length of this sequence, or beginIndex is larger than endIndex .

---

offsetByCodePoints

public int offsetByCodePoints(intindex,
                              intcodePointOffset)

Returns the index within this sequence that is offset from the given index by codePointOffset code points. Unpaired surrogates within the text range given by index and codePointOffset count as one code point each.

参数：

index - the index to be offset

codePointOffset - the offset in code points

返回：

the index within this sequence

抛出：

IndexOutOfBoundsException - if index is negative or larger then the length of this sequence, or if codePointOffset is positive and the subsequence starting with index has fewer than codePointOffset code points, or if codePointOffset is negative and the subsequence before index has fewer than the absolute value of codePointOffset code points.

---

getChars

public void getChars(intsrcBegin,
                     intsrcEnd,
                     char[]dst,
                     intdstBegin)

Characters are copied from this sequence into the destination character array dst . The first character to be copied is at index srcBegin ; the last character to be copied is at index srcEnd-1 . The total number of characters to be copied is srcEnd-srcBegin . The characters are copied into the subarray of dst starting at index dstBegin and ending at index:

 dstbegin + (srcEnd-srcBegin) - 1

参数：

srcBegin - start copying at this offset.

srcEnd - stop copying at this offset.

dst - the array to copy the data into.

dstBegin - offset into dst .

抛出：

NullPointerException - if dst is null .

IndexOutOfBoundsException - if any of the following is true:

• srcBegin is negative
• dstBegin is negative
• the srcBegin argument is greater than the srcEnd argument.
• srcEnd is greater than this.length() .
• dstBegin+srcEnd-srcBegin is greater than dst.length

---

setCharAt

public void setCharAt(intindex,
                      charch)

The character at the specified index is set to ch . This sequence is altered to represent a new character sequence that is identical to the old character sequence, except that it contains the character ch at position index .

The index argument must be greater than or equal to 0 , and less than the length of this sequence.

参数：

index - the index of the character to modify.

ch - the new character.

抛出：

IndexOutOfBoundsException - if index is negative or greater than or equal to length() .

---

substring

public String substring(intstart)

Returns a new String that contains a subsequence of characters currently contained in this character sequence. The substring begins at the specified index and extends to the end of this sequence.

参数：

start - The beginning index, inclusive.

返回：

The new string.

抛出：

StringIndexOutOfBoundsException - if start is less than zero, or greater than the length of this object.

---

subSequence

public CharSequence subSequence(intstart,
                                intend)

Returns a new character sequence that is a subsequence of this sequence.

An invocation of this method of the form

 sb.subSequence(begin,end)

behaves in exactly the same way as the invocation

 sb.substring(begin,end)

This method is provided so that this class can implement the CharSequence interface.

指定者：

接口 CharSequence 中的 subSequence

参数：

start - the start index, inclusive.

end - the end index, exclusive.

返回：

the specified subsequence.

抛出：

IndexOutOfBoundsException - if start or end are negative, if end is greater than length() , or if start is greater than end

---

substring

public String substring(intstart,
                        intend)

Returns a new String that contains a subsequence of characters currently contained in this sequence. The substring begins at the specified start and extends to the character at index end - 1 .

参数：

start - The beginning index, inclusive.

end - The ending index, exclusive.

返回：

The new string.

抛出：

StringIndexOutOfBoundsException - if start or end are negative or greater than length() , or start is greater than end .